The present invention relates to a signal converting method and circuit for a television signal, particularly to a scanning line converting method for a high resolutional television receiver and a circuit thereof.
In recent years, television receivers have been developed to a point that a high-resolutional image can be reproduced. Advanced techniques were being developed through research for replacing analog video signal circuits with digital signal circuits. Accompanying the replacement, techniques to process the television signal of the present system into a higher quality level have been proposed. The impairment of the picture quality of the television signal in the present system is caused mainly by interlaced scanning which is usually called 2:1 interlaced scanning and characterized by the following problems:
(1) Line flicker is generated around boundaries of lateral stripes pattern of the image;
(2) Structure of the scanning lines (since the number of scanning lines in each field may be as low 262.5 lines, becomes more significant for larger frames and details in the frames are blurred; and
(3) The currently available system fails to provide any improvement in overall resolution; a comb-filter is used to improve horizontal resolution, but vertical resolution is not improved at all.
To solve the problems described above, that is, to improve image quality, a system for doubling the number of the scanning lines by using line memories has been developed and is known as the 1:1 non-interlaced scanning with line interpolation system. There are two types of such system, that is, a same line interpolation and an average line interpolation, as will be described later. The average line interpolation system is described, for example, in Japanese Patent Application Laid-Open No. 79378/83. These systems can strike out the structure of the scanning lines in the frames. However, the systems have problems such that line flicker is emphasized rather than diminished or that resolution in the vertical direction is degraded on some video signal patterns.